Introduction to Optics
Including the tools and methods currently used by researchers and engineers, this book covers the essential concepts of comprehension and reports the great progress of the current knowledge in optics.
TABLE OF CONTENTS Introduction to Optics
Annex 12.A: Splitters and Couplers
In guided optics the electromagnetic energy is confined inside guides that have a very small cross section; a rather difficult problem arises if it is desired to transfer this energy to one or several other guides. It will be shown in Annex 12.C how fibers can be efficiently coupled to one another; the purpose of this annex is first to study how one guide, fiber, or integrated guide, can be coupled to one or two guides.
12.A.1 The Y-Junction
A signal can be introduced into a Y-junction, either by the "one-arm" side as in Figure 12.A.1(a), or by one of the two channels of the "two-arms" side, as in Figure 12.A.1(c). An accurate analysis is necessary, involving all the modes of propagation, including the leaky modes. In the case of single-mode guides and a symmetric Y-junction, the results are simple and can be described as follows:
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In the case of Figure 12.A.1(a), and if we omit the losses, the emerging signals are equal to one-half of the incident signal.
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In the case of Figure 12.A.1(c), a unit signal is introduced in the upper arm, no signal being introduced in the lower arm. The transmitted signal is only one-half of the incident signal; the other part goes to the cladding. In that case, a Y-junction has at least 3 db losses.
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In the case of Figure 12.A.1(b), a second Y-junction, very similar to the first one, has been placed as shown in the figure. When they arrive at the node of...
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